I. Field of the Invention
The present invention is concerned with filter elements in housings which are equipped with exchange devices. The present invention is also concerned with contamination protection and a method for the precipitation of materials which are injurious to health from the breathing air or processing air. The present invention is especially for ventilating systems wherein the process is connected with the process for comminution and removal of contaminated filter elements for the purpose of long-term storage in preferably subterranean deposits utilizing special waste containers, which waste containers are constructed in a round or angular shape.
II. Description of the Prior Art
In the case of such filter elements which are enriched or saturated with dangerous materials, it is customery, due to the extraordinary long-term effect, either to burn these filter elements at very high temperatures and turn them into ash or to put these filter elements into waste containers after reducing their volume with the application of pressure and to deposit them at subterranean places which are only accessible with difficulty. In either case this disposal method necessitates compliance with especially strict regulations concerning the protection of the environment.
It is known that various methods are utilized to satisfy these requirements; however, most of the removal procedures for contaminated filter elements are influenced to a very substantial extent by the desire to arrange the disposal processes in the most economical way without neglect of the requirements of the legislature. The filter maintenance and the necessary labor at the site of operation, which labor is concerned with the disposal of the filter in addition to the subsequent final removal by combustion or transport to a suitable place of deposit, by means of appropriate devices in compliance with the desired safety requirements, result in an effort which can be calculated in its magnitude and which effort is known to result in substantial expenses for the operator of the type of installation which was described above. Although the disposal expenses are not in any case even closely related to the procurement cost and to the actual usefulness and efficiency of the filter, the desire for safety in this field of application, which is based on legislation, cannot be disregarded.
With regard to the matter described above, the present general state of the art shows two methods for the removal of contaminated filter elements which are especially preferred and which are described in detail as follows:
1. Mechanical reduction of the volume of the contaminated air filter elements by means of shredder installations, impact mills or multiple saw and installations with subsequent compression by means of bailing presses or a pelletizing of the comminuted residual filter parts by means of suitable devices before storage in standardized 200 liter or 400 liter waste containers or waste drums.
2. Mechanical comminution for the disposal process of especially constructed air filter elements after separation of the filter frames, which consist of wood or metal, from the filter media by stamping or multiple separation by means of sawing or pressing. The subsequent mechanical separation of the individual filter parts serves for the direct discharge of those materials which can be oxidized by means of combustion in furnaces (1001.degree. C.), or in the latter case it serves for the centralized or decentralized deposition of the precompressed medium parts in waste containers which are provided for this purpose.
In order to perform such disposal processes, special housings with protective devices for the filter exchange and the appropriate and corresponding air filter elements were developed which, in case of a contamination depending on their type of construction and filter properties, can be exchanged in a more or less clumsy way and, finally, they can be removed as described. Filters with a low degree of contamination where the filter layers consists, for instance, of activated carbon or other absorption media are either equipped into waste containers until the contamination has diminished or they are combusted in appropriate waste combustion furnaces at high temperatures in case of the availability of these devices. All of the housings which should be utilized for this purpose are provided with appropriate filter change devices or filter exchange devices with protective bags, as described above, in order to protect the operating personnel during the exchange of the filter from contaminations or incorporations. For some filter elements construction for the nuclear field is mostly solved in such a way that the actual filter element consists of the rigid frame and a filter paper body in the shape of a compressible insert which can readily be released from the rigid frame. In this case the used filter unit which should be exchanged is first pulled out of the housing and is then separated from the rigid outer frame inside a transparent protective bag by means of a tear string. Following this, the volume of the contaminated parts is reduced in the known way by means of a crushing process or pressing process or by means of a sawing device or in a shredder or in an impact mill as a phase of preparation for the waste disposal, which is the next step. Prior to the process of filling, pouring or combustion, such filters must be comminuted to a fraction of their original volume for reasons of space usage. In many cases the remaining rigid filter frame, in case of a radioactive contamination, can be decontaminated and can be reused for the same purpose after some time.
A similar version is known in the U.S.A. In this case each of the angular filter elements consists of four tube-shaped parts of a block which are glued together or sealed or which can be compressed and which, as independent functional units, can be separated from each other, if this is necessary, by a stamping process and can be mechanically compressed.
Since the bulky and angular filter elements which were used to date could be placed after use, for the purpose of transport, into the round standard waste containers, only after they had been sawed apart or by making allowance for other difficulties as far as compression and comminution are concerned, and even then only with difficulty, there was a continuous search for new or similar solutions to the problem in order to be able to perform a simple and economical filter waste disposal without contamination of the environment.
The current state of the art is mainly critized for the unreasonably high expenditure for manual and mechanical pretreatment, and it is further critized for the very expensive processing devices and the protective measures which have to be used in order to be able to perform the described removal processes in an economical and space-saving way.
This complex situation is even more aggravated by the fact that the filter industry to date has usually manufactured angular filters for economical reasons in order to please the consumer; however, the barrel-shaped waste containers into which the used filters should be put after contamination are, in a completely contrasting way, manufactured in the form of a circle, also for reasons of economy and for some other undoubtfully advantageous reasons. However, this discrepancy in its entire magnitude is only completed by the inner measurements of the internationally standardized waste containers which are much too small as compared with the standardized outer measurements of the angular filter bodies which are customary and enjoy a world-wide distribution.
This situation could, of course, in a simple way be remedied in such a way that in the future the round waste containers will be manufactured somewhat larger or in a fitting shape, that is, in an angular shape or in a quadratic shape. On the other hand, it is still possible to manufacture the housings and the filter bodies in circular shape and in matching measurements with respect to the round waste containers in order to achieve an agreement; however, a more detailed examination has shown that the manufacture of angular containers is substantially more complicated and more expensive than the manufacturing of containers as they were up to date, especially if the same strength data and pressure data are desired for angular or box-shaped containers as for the round shapes of construction which were used to date. In addition, the cost for the manufacturing of the filters is increased if round filter elements should be utilized which would match the round containers instead of the use of the angular filter bodies; however, since for decades thousands of filter installations were used which were constructed, based on the angular or quadratic filter element dimensions which are internationally customary, a general conversion to the round air filter bodies in the future by the operators of filter installations is possible only if allowance can be made for high changeover costs and high investment costs concerning the existing air filter installations as well as the higher prices for filters. The same problem exists for the 200 liter standarized waste containers of round shape for the reception of contaminated filter wastes which are internationally customary to date. The 400 liter containers with their larger diameters were, in most cases, so far only used so that the 200 liter waste containers could be placed in them and sealed with concrete. For the intended purpose of placing the filter in these 400 liter containers for waste deposit, these containers would possibly be too expensive, since in the case of sealing with concrete a still larger container would then be necessary. Another reason for not changing the shape of the filter elements or the containers is the fact that the existing technical installations for the operation and maintenance of the existing removal installations, such as telekinetic manipulators or air locks, have been matched to the described types of constructions and dimensions for years and it would be very difficult to change this. The operators of nuclear installations as well as the manufacturers of containers, air filters and housings are presented with the same multiple cost problems which would occur if this situation should be changed in a rapid and general manner.
In this context it should also be mentioned that the contaminated waste of a nuclear installation which should be removed by means of oxidation or by means of deposition of course not always consists of used filter elements, but rather to a much larger extent it consists of various other materials which are part of the nuclear process and which have to be removed as waste. This also seems to be the reason for the fact that the disposal aspect of the filters is probably not taken serious enough.
The regulations concerning environmental matters, disposal matters and deposit matters have now become more strict. In some cases the cost for the maintenance of such installations has increased to such an extent due to new regulations that sometimes the entire technical process has been seriously reconsidered with regard to its economical aspects.
This is the reason why, at least as far as the filters are concerned, solutions to this problem are necessary which to begin with should be characterized by economic considerations, especially as far as the planning of such installations is concerned. The volume reduction installations and the comminution installations which were described above, such as, for instance, impact mills, separating devices, saws, shredder installations or bailing presses, necessitate the availability of large indoor spaces and rooms where these devices can be installed and which rooms are safeguarded with air locks and which rooms must be further safeguarded air tight and radiation protected with regard to the atmosphere. Furthermore, remote control devices are necessary which will start and control the mechanical process for the reduction of the volume and for the compression of contaminated filters in which case, of course, occasional repairs of contaminated machine parts should not be excluded.
The present state of the art of the comminution possibilities and compression possibilities of contaminated filter elements results, at best, in the reduction of volume of a ratio of 1:3. The extent to which the waste containers are filled independent of their capacity in liters is of an order of magnitude of maximum 65% to 70%, due to the very loose waste material and the volume of air that is entrapped in the filter material. Therefore, a complete utilization of the container volume in spite of the solidification is, at least, presently not yet possible. Whether in the near future a significant improvement can be achieved at all, considering the present state of the art of disposal of contaminated filter elements, is not clear at the present time.